1. Field of the Invention
The present invention relates generally to a mold for molding an optical element, in particular an ophthalmic lens, made of a thermosetting polymeric material, and more particularly using a reaction injection molding method (hereafter referred to as RIM).
2. Description of Related Art
Optical elements most often are made by molding and curing a liquid polymerizable composition in a suitable mold.
A method for using a polymerizable composition, hereafter referred to as reaction injection molding (or RIM), consists in introducing into the mold cavity or impression, a liquid polymerizable composition comprising at least two reagents that react with each other.
Reaction injection molding is a known method and a reaction injection molding method for contact lenses is especially described in the American patent U.S. Pat. No. 5,656,210.
For molding an optical element, it is necessary in order to obtain a transparent and structurally uniform end product that the mixing time combined with the filling time be shorter than the gelling time of the polymerizable composition. Reaction injection molding is a method wherein the mixing time is very fast. For this reason RIM makes it possible to use a polymeric material with very short gelling times.
However, in the context of optical element molding such as ophthalmic lenses, there still remain homogeneity and air-bubble entrapment problems within molded products especially due to this fast mixing time.